Light-weight and rigid weaving shafts are necessary for high-performance looms with up to 2000 fills/min. Acceleration values which permit the highest weft efficiency with an economical justifiable energy consumption are attainable only with light-weight weaving shaft heald systems. For a trouble-free weaving process, heald shafts must be as rigid as possible.
In the past, weaving shaft design has been adapted to the progressing increase in loom efficiency essentially by increasing the height of the heald shaft cross section for decreasing the severity of sagging. Since extruded sections are usually employed for the heald shafts, this approach is subject to limitations because of the associated considerable increase in the weight of the sections. A further increase in weaving shaft weight necessitates more powerful drive units for the weaving shafts and a considerably higher energy consumption, and thus renders further increases in weft efficiency uneconomical.
In DE 39 37 657 A 1, it is shown that weaving shafts with heald shafts consisting of carbon fiber or carbon fiber hybrid materials are currently employed for solving this problem. Decided advantages are light weight and high flexural strength because of the high elastic modulus, in comparison with an extruded aluminum section of equal height. Serious disadvantages of this proposal are the high price, which is several times that of a comparable aluminum section, as well as the unsolved problem of disposal of worn-out weaving shafts.
In the following references, that is, EP 496 054 A 1, DE 36 21 145 A 1, and DE 37 02 524 C 2, a different solution is proposed for the problem; that is, the upper and lower heald shafts of the proposed weaving shafts consist of a combination of steel sections, thin steel sheets, and light-weight frame structures. Weaving shafts produced from these sections are somewhat lighter than comparable aluminum weaving shafts, but the flexural strength is somewhat lower, and the price is about twice as high.
Finally, in U.S. Pat. No. 3,754,577, the addition of planking with rails or sheets of steel or carbon fibers in partial zones of extruded sections is proposed for increasing the flexural strength.
All of these proposed and in part practiced problem solutions ignore the state of the art, which implies that a beam on two supports should logically exhibit the highest geometrical moment of inertia in the zone of highest stresses.
In Austrian Patent 25 82 24, the insertion of a single hollow section of steel or aluminum as basis heald shaft with relatively low overall height is proposed for this purpose. By means of webs fastened to the back of the heald shaft, for instance, with screws or rivets, or by welding, whose height increases from the ends of the section toward the middle, higher flexural strength is envisaged and achieved with the least possible increase in weight. The web height in the middle can vary in correspondence with the length of the weaving shaft, or in correspondence with the load. However, this inherently ideal weaving shaft design also has not proved its worth in practice because of the cost, since the manufacturing process is evidently too expensive, and adaptation to match the wide variety of possible applications presents difficulties.
Another solution provides for one or more so-called central supports, which are frequently inserted between the upper and lower shaft sections for weaving shaft lengths as of 250 cm nominal width, if greater shaft weight is not tolerable. These central supports are an extremely unpleasant means of reducing the sag of the section, since they hinder manipulation in healding and frequently result in weaving defects and track during the weaving process.
The purpose of the present invention is to produce a weaving shaft which does not require a central support, even for large machine widths; at the same time, the weight of the weaving shaft must remain within the limits specified by loom and shaft machine manufacturers; finally, an economical manufacturing process which permits the use of recyclable materials is proposed.